1. Field of the Invention
The present invention relates to a vibration wave driven motor which causes a vibrating body and a member in contact with the aforesaid vibrating body to exert relative motion by the traveling vibration wave generated by the vibrating body. More particularly, the invention relates to a supporting device capable of supporting the vibrating body to be fixed to fixing members without any interference to its vibration.
2. Related Background Art
The vibration wave driven motor which utilizes traveling vibration waves has been in practical use recently, and the summary of its principle is given below.
To one face of a resilient ring type vibrating body having a total perimeter such as a certain length .lambda. times an integral number, there are fixed two groups of plural piezoelectric elements (hereinafter referred to as piezoelectric element group A and piezoelectric element group B) arranged in the peripheral direction to form a stator. These piezoelectric elements are arranged in each of the groups A and B at pitches of .lambda./2 with alternately inverted stretches. Also, there is arranged a deviation of .lambda./4 times an odd number between the groups A and B. For both of the A and B group piezoelectric elements, electrode films are provided respectively. When an alternating current voltage is applied to either one of the groups, i.e , only to the A group, for example, there is generated in the above-mentioned vibrating body along the total periphery thereof the standing wave of an out-of-plane vibration ((wavelength .lambda.) hereinafter referred to as standing wave A) which is a flexural vibration having antinode positions in the central portions of each of the piezoelectric elements in the aforesaid group A and at every other point .lambda./2 away therefrom as well as node positions in the central points between the aforesaid antinode positions. Then, when the AC voltage is applied only to the group B, there is likewise generated a standing wave (hereinafter referred to as standing wave B). However, the antinode and node positions thereof are deviated by .lambda./4 with respect to the aforesaid standing wave A. If an AC voltage of same frequency with time phase difference of .pi./4 is applied to both of the groups A and B simultaneously, then a flexural vibration having a traveling wave (wavelength .lambda.) which travels in the circumferential direction is generated as a result of the synthesis of the two standing waves. At this juncture, each of the points on the other face of the above-mentioned vibrating body which has a thickness is caused to create a kind of elliptic motion. Therefore, if a ring type movable member (rotor) is allowed to be in contact under pressure with the aforesaid other face of the vibrating body, then this movable member receives friction from the vibrating body in its circumferential direction so that it is driven to rotate The rotational direction thereof can be reversed by switching the phase difference of the AC voltage applied to both of the piezoelectric element groups A and B positive to negative. This has been the summary of the principle of a vibration wave driven motor of the kind.
On the other hand, it is not easy to fix the vibrating body for supporting the traveling vibration wave driven motor because there is no point in the vibrating body which is not displaced, i.e., there is no node of the vibration therein. Accordingly, the vibrating body is fixed to a fixing member through a flexible material such as felt.
Also, there is proposed a structure whereby to support the vibrating body by providing an auxiliary vibrating element such as disclosed in Japanese Patent Laid-Open Application No. 60-96183.
Furthermore, as disclosed in Japanese Patent Laid-Open Application No. 2-84079, a structure has been proposed in which a vibrating body is coupled by mounting members having an interval corresponding to {(.lambda./2)+n.lambda.} (where n is an integer including zero).
Nevertheless, with the conventional supporting structure such as using felt or other flexible materials, it is impossible to position the vibrating body accurately. Also, there is a disadvantage that the vibration insulation effect is reduced due to changes associated with the elapse of time, etc. Besides, it is almost impossible to support the reaction of the driving power although the pressure given to the rotor can be supported. As a result, it becomes necessary to provide another member such as disclosed in Japanese Patent Laid-Open Application No. 62-213585 in order to support the reaction exerted by the driving.
Also, in the supporting structure using the auxiliary vibrating element as disclosed in Japanese Patent Laid-Open Application No. 60-96183, it is necessary to make the length of the auxiliary vibrating element constant in the direction at right angles to the traveling direction of the traveling wave of the vibrating body. Accordingly, this occupies a large space, leading to a disadvantage that the total volume of the motor becomes great.
Also, for the structure whereby to couple the vibrating body by the mounting members having an interval corresponding to {(.lambda./2)+n.lambda.} to support it fixedly at its intermediate point as disclosed in Japanese Patent Laid-Open Application No. 2-84079, it is necessary to make its shape long and narrow, and to make it complicated to absorb the torsional stress of the coupling axis between them caused by the traveling wave. Furthermore, it is necessary for the beam portion of the mounting members to be in a motion close to rigidity. In this case, therefore, there is also a disadvantage that the dimension of the beam portion becomes great in practice because the driving frequency is usually as high as 20 KHz (in order to avoid the audible range).